Screw Gearing.
521
gear, with so many threads to the worm that it becomes a wheel.
Fig. 516 shews its application in a Multiple Drill where A A are
tfce drivers, and B B follow on the drill spindles r> D. The wheels
are here equal, and the teeth are inclined at 45° to the axis.
Epicyclic Wheel Trains, like worm gear, produce a high
ratio with few parts. Kinematically they are ordinary trains
where one wheel is the fixed link.
Case L — Fig. 517. Let A and L be in gearv with AL fixed.
If A make a minus rev. with relation to A L, L will have made
- plus revs., because — is the ratio of the train. Next fix A and
L L
put L out of gear. If now arm A L make one plus rotation two
things have happened : A has made one minus rev. relatively to
A L, and L has made one plus rev. relatively to A. Finally, put
A and L in gear, and give A L one plus rotation . L receives two
one plus rev* due to its connection with A L, and - plus
L
motions
revs, due to the relative minus turn of A
A, and «
I/s revs, «
both relatively to
A
+ =•
JL